BACKGROUND The City of Minneapolis ordered the owner of this apartment building to disconnect outdated rain leaders that still directed stormwater into the sanitary sewer. The property owner had one year to comply. In researching his options, he asked for advice from Friends of the Mississippi River, who referred him to Earth Wizards.

SITE SPECIFIC CONCERNS/GOALS Limited open space was available on the site to construct a rain garden large enough to manage stormwater from the 3500 square foot rooftop. The lower level of the apartment building along the main section of the proposed rain garden was 3’ below the existing grade elevation.  

SOLUTION/WORK COMPLETED We presented two conceptual designs to the property owner: a rain garden to handle a 10-yr, 24 hr storm event or a rain garden to hold a 100-yr, 24 hr storm event. The property owner wanted to take advantage of new stormwater utility fee credits that were available from the City and chose the 100-year rain garden to receive a 100 percent credit on his stormwater bill. Soil and infiltration tests were completed 4 feet below the proposed rain garden basin showing that the area could handle the necessary volume of water. We excavated a trench along the side of the building and installed a Miradrain Geotextile barrier to direct water away from the building. No new soils were imported to the site. Lasers were used to set grades throughout the site to ensure that the rain garden would receive the water equally.  The rooftop drain that had been hardlined into the sanitary sewer was now redirected through a pipe that exited to the side of the building into the rain garden.  Due to the size of the pipe and water velocities it would carry, a structure was installed to help prevent erosion and blowouts.  Overflows were installed to handle excess water to drain off the site during catastrophic rain events to prevent water from entering into the basement. We tilled the existing loamy soil and installed mulch throughout for the property owner to plant. A detailed plant design focused on plants that were easy to find locally, because the owner wanted to handle the installation and maintenance of plants.